The present invention relates to image forming apparatuses for printers, copying machines, etc., which form an image by irradiation with light carrying image information or by transmitting radiation through the original, and more particularly to image forming apparatuses for developing a latent image by pressurizing a light- and pressure-sensitive recording sheet on which the latent image is formed by exposure.
As conventional apparatuses of this type, using photosensitive recording sheets, there are diazo copying machines and systems utilizing the photographic developing process. In either case, some special chemicals must be provided exclusively for processes of developing and fixing a latent image which is formed on a photosensitive recording sheet by exposure. Such chemicals, which cannot be very easy to handle, entail various problems on the operation and maintenance of the apparatus.
As disclosed in U.S. Pat. Nos. 4,399,209 and 4,440,846, light- and pressure-sensitive recording sheets have been developed, as novel recording sheets, which obviate the aforesaid problems, and permit image formation without the use of chemicals. These sheets are recording media in which a layer of microcapsules and a layer of developer material are formed on a substrate. The microcapsules contain a chromogenic material such that their hardness varies according to the degree of exposure.
In image forming operation, the light- and pressure-sensitive recording sheet is exposed in accordance with the contents of the original to be copied, whereupon a latent image is formed on the sheet. Then, the microcapsules on the recording sheet are ruptured selectively, by means of a pressure roll, in accordance with their changed hardness. Thereupon, the chromogenic material and the developer material in the capsules react with each other, thereby developing a color image.
With use of the light- and pressure-sensitive recording sheet constructed in the aforesaid manner, the developing process does not require use of chemicals. Thus, there is a demand for the development of a compact image forming apparatus using such a recording sheet, as well as light- and pressure-sensitive recording sheets of a novel structure.
The pressure roll, which is used in the developing process, has the following problem. The chromogenic material from the ruptured microcapsules adheres to the roll, and soils the recording surface of the recording sheet when the roll pressurizes the sheet in the subsequent process, thereby lowering the quality of the image obtained.
In FIG. 4, upper and lower pressure roll 1 and 2 rotate individually in the directions indicated by arrows 3. A light- and pressure-sensitive recording sheet 4 is fed between the rolls 1 and 2, in the direction of the arrow. Before it is delivered to the rolls 1 and 2, the recording sheet 4 is formed with a latent image, at a latent-image forming section (not shown). Then, the sheet 4 is pressurized between the rolls 1 and 2, whereupon the microcapsules on the sheet 4 are ruptured according to their hardness As a result, the chromogenic material from the capsules reacts with the developer material, thereby developing a color image, varied in density, on the recording sheet.
In this case, part of the developed coloring material adheres to that pressure roll which faces the recording surface, thus causing the aforementioned problem.
In order to remove the coloring material adhering to the pressure roll, a conventional pressure roll mechanism is constructed as shown in FIG. 5 or 6. In FIG. 5, a roll cleaner 6 is disposed in contact with the surface of the pressure roll 1. The cleaner 6 is composed of a small roll and a felt member wound thereon. The felt member serves to wipe the surface of the pressure roll 1. Since the felt itself soils, it must be replaced or maintained as required or periodically. A conveyor mechanism 7 is used to transport the recording sheet 4.
In FIG. 6, a felt cleaner 8, a pawl 9, and a receiver 10 are arranged in contact with the surface of the pressure roll 1. The cleaner 8 wipes the surface of the roll 1, the pawl scrapes residual matter from the roll surface, and the receiver 10 receives the scraped matter. This conventional pressure roll mechanism requires cleaning of the receiver 10, as well as replacement and maintenance of the cleaner 8.